Crews spent about six hours trying to locate Dr. Peter Hertzak, a 65-year-old physician from suburban New Orleans, after his twin-propeller Cessna 421C went down Thursday about 120 miles west of Tampa, Fla.

The plane was headed from Slidell, La., to Sarasota, Fla., when it started flying around in circles for hours.

Air Force jets were dispatched to look into the plane after the pilot failed to respond to numerous communication attempts by controllers.

The jet crews were unable to see the pilot because of fog and icing that obscured the plane's windows, Coast Guard officials said. The icing is seen as a possible sign that the aircraft lost cabin pressure and the pilot was rendered unconscious.

There was no sign that the pilot, believed to be the only person aboard, survived the crash. The search has been called off pending further developments, the Coast Guard said Friday.

The U.S. Coast Guard is trying to recover the pilot after his plane went down after flying in circles for nearly three hours. NBC's Pete Williams reports.

"This is one of those unfortunate cases where even though we stood ready to respond, we were unable to effect a rescue," Lane Carter, command duty officer for the Coast Guard’s 8th District command center, said in a news release.

Hertzak was a cosmetic surgeon and OB-GYN from New Orleans and was believed to have been flying to Florida for pleasure, according to media reports.